- Study: Dogs’ fearfulness has a strong link to aggressive behaviour, with fearful dogs many times more likely to behave aggressively. Moreover, older dogs are more likely to behave aggressively than younger ones. One of the potential reasons behind this can be pain caused by a disease. https://www2.helsinki.fi/en/news/life-science-news/dogs-aggressive-behaviour-towards-humans-is-often-caused-by-fear 27 comments science